Lithographic apparatus, contaminant trap, and device manufacturing method

ABSTRACT

A lithographic apparatus includes a radiation system including a radiation source for the production of a radiation beam, and a contaminant trap arranged in a path of the radiation beam. The contaminant trap includes a plurality of foils or plates defining channels which are arranged substantially parallel to the direction of propagation of said radiation beam. The foils or plates are oriented substantially radially with respect to an optical axis of the radiation beam. The contaminant trap is provided with a gas injector which is configured to inject gas at least at two different positions directly into at least one of the channels of the contaminant trap.

FIELD

The invention relates to a lithographic apparatus, a contaminant trap, adevice manufacturing method, and a device manufactured thereby.

DESCRIPTION OF THE RELATED ART

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.including part of one, one, or several dies) on a substrate (e.g. asilicon wafer). Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network ofadjacent target portions that are successively patterned. Knownlithographic apparatus include so-called steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beamin a given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti-parallel to this direction. Itis also possible to transfer the pattern from the patterning device tothe substrate by imprinting the pattern onto the substrate.

WO99/42904, incorporated herein by reference, discloses a contaminanttrap, called a filter, for trapping source debris. Said knowncontaminant trap comprises a plurality of foils or plates, which may beflat or conical and are arranged in a radial direction from theradiation source. The source, the filter and the projections system maybe arranged in a buffer gas, for example krypton, whose pressure is 0.5Torr. The contaminant particles then take on the temperature of thebuffer gas, for example room temperature, thereby sufficiently reducingthe particles' velocities before they enter the filter. The pressure inthe known contaminant trap is equal to that of its environment. Thistrap is arranged at 2 cm from the source and its plates have a length,in the propagation direction of the radiation, of at least 1 cm andpreferably 7 cm. This design requires relative large and thus costlycollecting and guiding/shaping optics to bundle and shape the sourceradiation and guide it to the mask.

European Patent Application No. 1203899.8 describes a further improveddevice for trapping debris, such as may be emitted by a plasma source orfrom resist exposed to EUV radiation. This document describes acontaminant trap comprising a first set of plate members arrangedparallel to the direction of propagation of the radiation beam, and asecond set of plate members that is arranged parallel to the directionof propagation. The first and second sets are spaced apart from anotheralong an optical axis of the radiation beam. There is a space betweenthe first and second set of plate members. Flushing gas is supplied tothat space to provide a high gas pressure to trap the contaminantparticles. The two sets of plate members are designed such that leakageof the gas is minimized and that the gas pressure outside the trap iskept low. However, still, an amount of EUV is also absorbed by this gaswith relatively high pressure.

SUMMARY

It is an aspect of the present invention to further improve trappingand/or mitigating debris while having a relatively simple design for thecontaminant trap.

According to an aspect of the invention, there is provided alithographic apparatus comprising: radiation system including aradiation source for the production of a radiation beam; and acontaminant trap arranged in a path of the radiation beam, thecontaminant trap comprising a plurality of foils or plates definingchannels which are arranged substantially parallel to the direction ofpropagation of said radiation beam, wherein the foils or plates areoriented substantially radially with respect to an optical axis of theradiation beam, and wherein the contaminant trap is provided with a gasinjector which is configured to directly inject gas at least at twodifferent positions into at least one of the channels of the contaminanttrap.

In an aspect of the invention, a lithographic apparatus comprises: aradiation system including a source for the production of a radiationbeam; and a contaminant trap arranged in a path of the radiation beam,the contaminant trap comprising a plurality of foils or plates definingchannels which are arranged substantially parallel to the direction ofpropagation of said radiation beam, wherein the contaminant trap isprovided with a gas supply system which is configured to directly injectgas at least at two different positions into each of the channels of thecontaminant trap.

According to an aspect of the invention, there is provided alithographic apparatus comprising: a radiation system including a sourcefor the production of a radiation beam; and a contaminant trap arrangedin a path of the radiation beam, the contaminant trap comprising aplurality of foils or plates defining channels which are arrangedsubstantially parallel to the direction of propagation of said radiationbeam, wherein the contaminant trap is provided with a gas supply systemwhich is configured to inject gas directly into each of the channels ofthe contaminant trap. The gas supply system is configured to achieve:

∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m)in each of the channels, wherein p(x) is the pressure —in Pa—at locationx in the channel, x1 is the position —in m—of the entrance of thechannel and x2 is the position —in m—of the gas outflow opening(s) inthe channel.

Also, in an aspect of the invention, there is provided a contaminanttrap, configured to be arranged in a path of a radiation beam duringuse, the contaminant trap comprising a plurality of foils or platesdefining radiation transmission channels which substantially transmitthe radiation beam during use, wherein the foils or plates are orientedsubstantially radially with respect to each other, and wherein thecontaminant trap is provided with a gas supply system which is arrangedto inject gas directly at least at two different locations into at leastone of the channels of the contaminant trap.

In another aspect of the invention, a contaminant trap, which isconfigured to be arranged in a path of a radiation beam during use,comprises a plurality of foils or plates defining radiation transmissionchannels which substantially transmit the radiation beam during use,wherein the contaminant trap is provided with a gas supply system whichis arranged to inject gas directly at least at two different locationsinto at least one of the channels of the contaminant trap, wherein thegas supply system is configured to achieve:

∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m)in each of the channels, wherein p(x) is the pressure at location x inthe channel, x1 is the position of the entrance of the channel and x2 isthe position of the gas outflow opening(s) in the channel.

An aspect of the invention provides a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substrate,wherein: a source is provided to produce a radiation beam; and acontaminant trap is provided in a path of the radiation beam, whereinthe contaminant trap comprises a plurality of foils or plates definingradiation transmission channels which substantially transmit saidradiation beam, wherein the foils or plates are oriented substantiallyradially with respect to an optical axis of the radiation beam, andwherein gas is directly injected at least at two different positionsinto at least one of the channels of the contaminant trap.

An aspect of the invention provides a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substrate,wherein: a source is provided to produce a radiation beam; and acontaminant trap is provided in a path of the radiation beam, whereinthe contaminant trap comprises a plurality of foils or plates definingchannels which are arranged substantially parallel to the direction ofpropagation of said radiation beam, and wherein gas is directly injectedat least at two different positions into each of the channels of thecontaminant trap.

Further, the invention provides a device that is manufactured by anabove-mentioned method, or by an above-mentioned apparatus according tothe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 schematically depicts part of the lithographic apparatusaccording to a further embodiment of the invention;

FIG. 3A is a perspective view of a first embodiment of a contaminanttrap which includes gas injection capillaries;

FIG. 3B is a similar view as FIG. 3B, without showing the foils;

FIG. 4 is a front view of the first embodiment of the contaminant trap,without showing the capillaries;

FIG. 5 is a detail of a circumferential cross-section of the firstembodiment of the contaminant trap;

FIG. 6 a cross-section over line VI-VI of FIG. 5;

FIG. 7 is a partially opened side view of the first embodiment, showingorientations of two of the capillaries with respect to the source andcollector, as well as a number of radiation paths in more detail;

FIG. 8 schematically depicts a detail of the embodiment of FIG. 2,showing an optional helium supplier near opposite sides of the radiationsource and the contaminant trap;

FIG. 9A is a perspective view of a second embodiment of a contaminanttrap, which includes gas injection rings;

FIG. 9B is a similar view as FIG. 9A, without showing the foils;

FIG. 10 is a side view of a detail of a gas supply ring of the secondembodiment of the contaminant trap;

FIG. 11 is a cross-section over line XI-XI of FIG. 10;

FIG. 12 is a side view of one of the two groups of gas supply ringsections of an alternative gas injector of the second embodiment of thecontaminant trap;

FIG. 13 is a perspective view of the group of ring sections shown inFIG. 12;

FIG. 14 shows a detail of an alternative embodiment of the invention;and

FIG. 15 shows a detail of an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises: an illuminationsystem (illuminator) IL configured to condition a radiation beam B (e.g.UV radiation or other radiation); a support structure (e.g. a masktable) MT constructed to support a patterning device (e.g. a mask) MAand connected to a first positioner PM configured to accurately positionthe patterning device in accordance with certain parameters; a substratetable (e.g. a wafer table) WT constructed to hold a substrate (e.g. aresist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters; and a projection system (e.g. a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g. comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a reflective type (e.g. employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g. employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.Also, a contaminant trap 10, 110 can be provided downstream with respectto the source SO, for example to trap contamination that emanates fromthe source SO, in particular a radiation source that generates EUVradiation. The source SO and the illuminator IL, together with the beamdelivery system BD and/or contaminant trap 10, 110 if needed, may bereferred to as a radiation system.

The illuminator IL may comprise an adjuster for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator and acondenser. The illuminator may be used to condition the radiation beam,to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF2 (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam B. Similarly, the first positioner PMand another position sensor IFI can be used to accurately position themask MA with respect to the path of the radiation beam B, e.g. aftermechanical retrieval from a mask library, or during a scan. In general,movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner), themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the mask MA, the mask alignmentmarks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PS. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 depicts a portion of a lithographic apparatus according toFIG. 1. FIG. 2 shows in particular an arrangement of a radiation sourceSO, a contaminant trap 10, 110 and a radiation collector CO. Thecontaminant trap 10, 110 is located between said radiation source SO andthe radiation collector CO. The radiation collector can include, forexample, mirror surfaces that receive radiation from the radiationsource during use.

As shown schematically, during use, a radiation beam R can originatefrom source SO and can propagate into the direction of a contaminanttrap 10, 110, which is arranged in the path of that radiation beam R. Itshould be borne in mind that radiation can propagate from the source invarious directions, for example in a diverging manner (see FIG. 7). Thecontaminant trap 10, 110 can include a large number of substantiallyparallel channels Ch (for example as shown in FIGS. 3-7) which areconfigured to transmit most of the radiation beam R from the source SOtowards the radiation collector CO. Also during use, contaminatingparticles CP can move from the source SO towards and into thecontaminant trap 10, 110. Such contamination can include, for example,ions and/or atoms that can originate from the radiation source SO. Ithas been found that in operation much less contaminating particles CPleave the contaminant trap 10, 110 in the direction of propagation ofthe radiation beam R in comparison with the number of contaminatingparticles entering the contaminant trap 10, 110 in the general directionof propagation of the radiation beam.

In the embodiment of FIG. 2, the lithographic apparatus is provided witha gas supply system GS, 12, 13, 112, 113 which is arranged to inject atleast a first gas directly into at least one of the channels of thecontaminant trap 10, 110. The gas supply system can include one or moregas sources GS, a gas injector or manifold 12, 112 (see below) to injectthe gas directly into the channel, and one or more gas supply lines 13,113 which couple the gas source GS to the gas injector 12, 112. Such gassupply lines 13, 113 and gas sources GS can be constructed in variousways, as will be clear to the skilled person. In a further aspect, atleast a first gas source GS can be provided, which is connectable orconnected to the gas injector 12, 112 to supply at least a first gasthereto. For example, the first gas can be argon, or an other suitablegas. Preferably, the gas injector 12, 112 is configured to substantiallynot obstruct the transmission of radiation that is transmitted from theradiation source SO towards the mirror surfaces of the radiationcollector CO during use.

Besides, the apparatus can be configured to provide a further gas-flowCG between the source and the contaminant trap 10, 110, which gas-flowCG can flow substantially across the radiation exiting the source SO, ina direction substantially transverse with respect to the direction ofpropagation of the radiation beam R, or in an other suitable direction.Such further gas flow, or counter gas flow, can counteract or preventthe above-mentioned at least first gas to enter the radiation source SO(see FIG. 8). Also, such further gas flow CG can further capturecontamination that emanates from the radiation source. For example, theapparatus can include at least one gas supplier 20 which is configuredto inject at least a second gas into a location near a butt-end of thecontaminant trap 10, to catch, divert and/or decelerate first gas whichflows out of that butt-end. Such a gas supplier is schematicallydepicted in FIGS. 2 and 7 by dashed lines 20. This gas supplier 20 canbe configured in various ways. For example, as is shown in FIG. 8, thisgas supplier 20 can be mounted onto or form part of a wall portion ofthe radiation source SO. In an aspect of the invention, the second gasis helium.

Also, the apparatus can be provided with a drain system which isarranged to produce a transverse flow of gas in a radial and outwardsdirection with respect to the direction of propagation of the radiationbeam and along an entrance of the contaminant trap, such that thetransverse flow of gas comprises at least part of the injected gas. Thedrain system can be configured in various ways. For example, the drainsystem can include one or more vacuum pumps VP that can be configured topump down the environment of the contaminant trap 10 during use. Thedrain system can also be configured in a different manner.

FIGS. 3A, 3B, 4-7 show a first embodiment of a contaminant trap 10, thatcan be used in the above-mentioned lithographic apparatus. This firstcontaminant trap embodiment 10 comprises a plurality of static foils orplates 11 defining radiation transmission channels Ch. The foils orplates 11 can be substantially solid foils or plates 11 that do notcontain apertures by themselves. The channels Ch can be arrangedsubstantially parallel to the direction of propagation of said radiationbeam during use. Besides, in the present embodiment, the foils or plates11 are oriented substantially radially with respect to an optical axis Yof the radiation beam R.

The foils or plates 11 can be regularly and symmetrically distributedaround the center axis of the trap 10, such that the channels Ch havesubstantially the same volume. The foils or plates 11 can be connectedto each other, for example, at radially outer sides by an outer foilconnector 18 a. The foils or plates 11 can be connected directly to eachother at radially inner sides, or for example, by an inner foilconnector 18 b. Said foil connectors 18 a, 18 b can be constructed invarious ways, for example as substantially closed or solid cylindricalor truncated conical walls (see FIGS. 3A and 3B), or in a differentmanner. In the present embodiment, each radiation transmission channelCh of the contaminant trap 10 is substantially surrounded by neighboringfoils or plates 11 and by the outer and inner foil connectors 18 a, 18b, when viewed in a transversal cross-section (see also FIG. 4). In anaspect of the invention, the contaminant trap 10 can include a largenumber of relatively narrow or slit-like channels, for example at leastabout 100 channels, or at least about 180 channels. In that case, eachof the channels Ch can be oriented substantially radially with respectto the optical axis Y of the radiation beam R during use.

The contaminant trap 10 is provided with an above-mentioned gas injector12 which is configured to directly inject gas at least at two differentpositions into at least one of the channels Ch of the contaminant trap.In the present embodiment, this gas injector is configured to directlyinject gas at least at two different positions into each one of thechannels Ch of the contaminant trap 10.

In the embodiment of FIGS. 3A, 3B, 4-7, the gas injector 12 includesthree substantially concentric, spaced-apart, ring shaped (circular) gassupply tubes 12A, 12B, 12C, herein also called gas supply rings 12.These gas supply rings 12A, 12B, 12C are also substantially concentricwith respect to said optical beam axis Y. Each of these rings 12 isconnected to different gas outflow openings which are associated withdifferent channels Ch. To this aim, each of the concentric gas supplyrings 12A, 12B, 12C is provided with a plurality of gas injectioncapillaries 14A, 14B, 14C, or similar thin tubes or gas supply needles.The capillaries (needles) can be used for a controlled supply flow ofgas to determined locations of the channels Ch. Each of the gasinjection capillaries 14A, 14B, 14C extends into one of the radiationtransmission channels Ch (see FIGS. 3B, 5 and 6), such that each of thechannels Ch is provided with three of these gas injection capillaries 14(see FIG. 6). The capillaries 14 can be positioned, for example, alongradial directions at “dead” angles. Also, the wall of each of thecapillaries 14 can include a plurality of spaced-apart gas outflowopenings 17 (see FIG. 5-7).

FIG. 5 shows a detail of a number of neighboring channels Ch(1)-Ch(6),depicting the respective outer capillaries 14A in a front view, and FIG.6 shows a cross-section of one of these channel parts Ch(6), depictingthe respective group of three capillaries 14A, 14B, 14C that areconfigured to inject gas into that channel Ch(6). In an embodiment ofthe invention, a distal end of each capillary 14 can be closed (see FIG.6). As follows from FIG. 7, the capillaries 14 of the gas injector 12are configured to substantially not obstruct transmission of radiationfrom the radiation source SO towards the mirror surfaces of theradiation collector CO.

Therefore, in the embodiment of FIGS. 3A, 3B, 4-6, the gas injectorcomprises a plurality of groups of spaced-apart outflow openings,provided by three groups of capillaries 14A, 14B, 14C, wherein eachgroup of spaced-apart outflow openings 17A, 17B, 17C is associated withone of said channels Ch to supply gas to that channel. In the presentembodiment, outflow openings 17A, 17B, 17C of each group of spaced-apartoutflow openings are located at different radial positions with respectto the optical axis Y of the radiation beam, since the respectivecapillaries 14A, 14B, 14C extend at different radial positions in thecontaminant trap. Besides, the outflow openings of each group ofspaced-apart outflow openings can be located at different and/orsubstantially the same axial positions with respect to the optical axisY of the radiation beam. Also, the outflow openings of each group ofspaced-apart outflow openings can be connected to different gas supplylines 13, via the gas supply rings 12A, 12B, 12C, for example toindependently regulate the amounts of gas that are injected via thedifferent outflow openings. On the other hand, the outflow openings ofthe three groups of spaced-apart outflow openings can be connected tothe same gas supply line 13.

The outflow openings 17 of the capillaries 14 can be configured invarious ways. In an aspect of the invention, a relatively large numberof relatively small outflow openings 17 is provided, to provide arelatively uniform flow of gas in the channels Ch at the same overallamount of gas injected into the trap 10. For example, at least one ofthe outflow openings 17 can include a supersonic nozzle, which isconfigured to inject a supersonic gas stream into the respective channelCh. Alternatively, such supersonic micro-nozzles can be placed directlyon edges of the foils or plates 11, or at different locations. Also, thegas injector can be arranged to inject gas in a different direction thana direction of propagation of the radiation beam through the contaminanttrap 10. In the present embodiment, the gas injector is arranged toinject gas in substantially transverse directions into the channels Ch,via the gas outflow openings 17 of the capillaries 14. Each of theoutflow openings 17 can have, for example, a minimum diameter of about0.0018 mm+/−0.002 mm, or another diameter. Outflow openings 17 can bemanufactured, for example, using laser cutting or a different technique.Preferably, edges of these openings include sharp edges that are free ofburrs.

In an embodiment of the invention, the gas supply system can beconfigured to supply gas into at least one of the channels Ch of thecontaminant trap under gas flow choke conditions. In that case, a steadygas injection can be obtained, particularly when gas is injected via aplurality of the outflow openings 17 under choke conditions. Suchconditions can be achieved, for example, when the environment pressureof a capillary 14 is about a factor 2 or more lower than insidepressure, particularly when the first gas is argon. Also, a pressuretransition through each outflow-opening 17 can be abrupt to achieve achocking effect. For example, to this aim, the gas supply system caninclude at least one gas supply tube, or capillary 14, having a wallwhich includes a plurality of the gas outflow openings 17, wherein alength H of each gas outflow opening 17, measured through the tube wall,is larger than a cross-section or diameter G of that gas outflowopening. This will be explained below with respect to FIG. 11. Thedimensions of the capillaries 14 and outflow openings 17 can be designedsuch, that the resulting gas injector is sufficient rigid to maintainits form at operation temperature, and that the gas injector can resisttension created therein by overpressure.

In an aspect of the invention, the gas injector 12 and the gas supply GScan be configured to achieve:

∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m)during use, wherein p(x) is the pressure at location x in the channel,x1 is the position of the entrance for radiation of the channel and x2is the position of the gas outflow opening(s) in the channel. As isshown in the figures, during use, the entrance of each channel Ch of thecontaminant trap can be directed towards the radiation source SO, toreceive radiation therefrom. It has been found that when

∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m),a good contamination trapping can be achieved by the contaminant trap10, for example to trap one or more high energetic atomic debriscomponents. Besides, since gas can be injected internally into thechannels Ch of the contaminant trap 10, the above-mentioned equation canbe achieved, wherein the pressure outside the contaminant trap 10 can bekept sufficiently low.

The embodiment of FIGS. 2-8 can be used in a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substrate,wherein: the source SO is provided to produce a radiation beam; and thecontaminant trap 10 is provided in a path of the radiation beam. Then,the foils or plates of the trap 10 are oriented substantially radiallywith respect to the optical axis of the radiation beam Y, so that theradiation beam can pass through the trap 10 to the collector DB (seeFIG. 7). A first gas, for example argon, is directly injected by theinjection capillaries 14 at different positions into each of thechannels Ch of the contaminant trap 10. In the present embodiment, thefirst gas is being injected in injection-directions which notnecessarily coincide with the radiation propagation direction, but whichdirections can provide an efficient filling up the channel. The amountof the first gas that is injected into each channel Ch can be such, thatit can capture debris emanating from the radiation source SO relativelywell. For example, as follows from the above, the gas can be injectedsuch, that the equation

∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m)(or in simpler terms: that p.d>1 Pa.m) is satisfied in the channel Ch.When argon is used as a first gas, the amount of argon that is injectedinto each foil trap channel can be, for example, about 10⁻⁶ kg persecond or more, or on the other hand for example a lower amount such asabout 10⁻⁶ kg per second or less. When the contaminant trap includes alarge number of slit-like channels Ch, for example at least 100 channelsCh, the injected first gas can achieve the above-mentioned equationrelatively well. After being injected, the first gas can leave thecontaminant trap 10 at one or both ends, wherein the pressure outsidethe contaminant trap 10 can be held at a usually desired low value.

Also, as is shown in FIG. 8, a transverse flow of a second gas CG can beproduced in a radial and outwards direction with respect to the generaldirection of propagation Y′ of the radiation beam and along the entranceof the contaminant trap 10, such that the transverse flow of gascomprises at least part of the injected gas. In the present embodiment,the second gas provides a crossing gas flow across the radiation beamand in a direction substantially transverse the direction of propagationof the radiation beam. The second gas can prevent the first gas fromentering the radiation source SO. The second gas can be, for example,helium. It has been found, that helium can protect the radiation sourceSO against the first gas entering the source SO relatively well, whereinthe helium can be used at relatively high pressures without negativelyaffecting the operation of the radiation source SO too much.

During use of the embodiment of FIGS. 2-8, the first gas can be injectedat three different radial positions in each of the channels Ch, viewedfrom the optical axis of the radiation beam, via pluralities ofrelatively small gas outflow openings 17A, 17B, 17C. Therefore, arelatively large amount of gas can be injected relatively uniformly intothe channel Ch. Preferably, the first gas is injected into the channelsunder choke conditions. For example, to this aim, the gas pressureinside each capillary 14 can be at least twice the gas pressure in therespective channel Ch, downstream of the outflow openings 17.

Filling up the inter-foil gaps or channels Ch using the internal gassupply openings 17 can enable to achieve a value of the pressureintegral over the radial distance within the foil trap, p(x)dx, that issufficient for thermalization and subsequent trapping of the mostenergetic atomic debris component, for example debris that canessentially contribute in degradation of EUV collection optics. Sincegas can be injected directly into the contaminant trap 10, a relativelylarge p(x)dx pressure integral value can be obtained, wherein anunacceptable rise of pressure outside the contaminant trap 10 can beprevented. This can be advantageous, for example, in an EUV source zonewhich includes the radiation source SO, where a maximum pressure ofargon is 0.5 Pa, particularly when the radiation source is a Sn source.Besides, during use of the present embodiment, the internal gasinjection in each channel Ch can generate a gas flow with a high dragforce in the narrow inter-foil channels Ch, providing a relatively highpressure therein. Outside the channel Ch, the drag force can disappear,which results in gas acceleration and drop of pressure.

Also, internal injection can provide a relatively high pressure gas fillin the channel, which, due to the drag force (it can essentiallyincrease with pressure) can slowly leak out of the channel.

Additional protection of the radiation source SO from a fraction of thegas flowing out of channels Ch can be performed using the mentionedcounter gas CG flow provided by the second gas. This counter gas flowcan have a low static pressure and a high velocity to maintain a totalcounter pressure at a safe distance from the source SO. As a result, aremaining outflow fraction of the first gas can be re-directed to thedrain system. Preferably, during use, a maximally admissible pressureintegral p(x).dx over the length of the contaminant trap can beachieved, which pressure integral can be limited by a desired amount ofradiation transmission of the radiation beam through the contaminanttrap 10. Also, preferably, during use, a high contrast of pressuredistribution inside and outside the contaminant trap 10 can be achieved,providing a desired low pressure in the source zone that includes theradiation source SO. Besides, an efficient use of gas flow can beobtained.

FIGS. 9A, 9B, 10, 11 depict a second embodiment of a contaminant trap110, that can also be used, for example, in an above-mentionedlithographic method. The second embodiment 110 differs from the firstcontaminant trap embodiment 10, in that the gas injector does notinclude gas injection capillaries.

In the second embodiment, the gas injector includes three substantiallyconcentric circular gas supply rings 112, wherein each of these rings112 includes a plurality of the gas outflow openings, as is shown inFIG. 12. The gas supply rings 112 are connected to the above-mentionedgas source GS via one or more gas supply lines 113. The rings 112 aremounted through the foils or plates 111. Also, each of the concentricgas supply rings 112 extends substantially perpendicular through thefoils or plates 111. To this aim, the foils or plates 111 can beprovided with apertures through which the gas supply rings 112 extend.Each of the gas supply rings 112 includes gas outflow openings 117 toinject gas into respective channels Ch. As is shown in FIG. 11, a lengthH of each gas outflow opening 117, measured transversally through thetube wall of the respective gas supply ring 112, is larger than across-section or diameter G of that gas outflow opening 117. This canlead to choke conditions during use, depending on the pressure drop overthe outflow opening, as has been explained above. Also, in the secondtrap embodiment 110, in each channel Ch the spaced-apart outflowopenings 117 are located at different radial positions with respect tothe optical axis of the radiation beam Y, to provide a relativelyuniform distribution of injected gas.

FIGS. 12 and 13, show a first part of an alternative embodiment of a gasinjector, that can be implemented in the second contaminant trapembodiment 110. In the alternative embodiment of FIGS. 12 and 13, thegas injector includes two sets of four substantially concentric gassupply ring sections 112A′, 112B′, 112C′, 112D′. Only one of the sets isshown. The two separate groups of substantially concentric gas supplyring sections are configured, to form together substantially closedrings, similar to the supply rings 112 of the gas injector as depictedin FIG. 9B. After mounting, each of the concentric gas supply ringsections 112A′, 112B′, 112C′, 112D′ extends substantially perpendicularthrough the foils or plates 111 of the contaminant trap 110. By such adivision of the gas injector into two segments, a more simple andstraight-forward mounting of the gas injector into the contamination canbe obtained.

In the alternative gas injector, each of the gas supply ring sections112A′, 112B′, 112C′, 112D′ comprises spaced-apart gas outflow openings(not shown) which are associated with the different radiationtransmission channels Ch to supply gas to these channels Ch. The fourgas supply ring sections 112A′, 112B′, 112C′, 112D′ of each set ofsections are connected to each other by substantially radially extendingconnecting parts 113. These substantially radially extending connectingparts are provided with four different gas supply lines to supply gas tothe different gas ring sections separately. Also, the connecting partsconnect the ring sections 112A′, 112B′, 112C′, 112D′ of each group ofconcentric gas supply ring sections 112A′, 112B′, 112C′, 112D′ to eachother at about their middles, measured along their circumferences (seeFIG. 13). This can provide a stable mounting of the ring sections 112A′,112B′, 112C′, 112D′. The present embodiment of the gas injector can beused to directly inject one or more gasses at least at four differentpositions into each of the channels Ch of the contaminant trap 110.Since the outflow openings of each group of spaced-apart outflowopenings are connected to different gas supply lines 113A, 113B, 113C,113D, the amounts and/or types of gas that are fed to the different ringsections can be independently regulated, for example using suitable flowcontrollers and/or gas sources. Such a regulation of gas flows and/orgas types can be directed to optimise the trapping of contamination inthe contaminant trap 110, as will be clear to the skilled person.

In FIGS. 12 and 13, the outflow openings of each group of spaced-apartoutflow openings are located at different radial positions with respectto the optical axis of the radiation beam (see FIG. 13). Also, theoutflow openings of each group of spaced-apart outflow openings arelocated at different axial positions with respect to the optical axis ofthe radiation beam (see FIG. 12). Location of spaced-apart outflowopenings at different axial positions can enable to achieve optimalinjection point to reach large pd integral values.

FIG. 14 shows a detail of an embodiment of a contaminant trap. Theoverall construction of this embodiment can be similar to theconstruction of one or more of the above-described embodiments of FIGS.3-13. In the embodiment of FIG. 14, one or more of the gas injectioncapillaries 214 of the gas injector, or gas supply system, extend withinone or more of the foils 211 of the trap to supply gas to selectedinjection points. Only part of one of the foils 211, which includes onecapillary 214, is depicted in FIG. 14. The capillary 214 of the foil 211can extend to one or more selected injection points or outflow openings(not shown in FIG. 14) to inject gas into one or more adjoining channelsof the contaminant trap. The capillary 214 of the foil 211 can bemanufactured in various ways, for example by a foil aperture that iscovered on both sides by thin foil strips 290.

FIG. 15 shows a detail of an embodiment of a contaminant trap. Theoverall construction of this embodiment can be similar to theconstruction of one or more of the above-described embodiments of FIGS.3-14. In the embodiment of FIG. 15, a group of main foils 311A definesthe channels, wherein one or more additional foils 311B are installedbetween the main foils 311A in at least one of the channels. In theembodiment of FIG. 15, one additional radial foil 311B has beeninstalled in each channel. For example, the additional foils can beincluded in a peripheral zone of the contaminant trap. The additionalfoil 311B can split the basic inter-foil spaces between the main foils311A, which can be wide at large distances from the source SO, in twomore narrow channels with a higher drag (friction) force for gas,resulting in increase of the pd-integral. The additional foils can besufficiently remote from the source SO, so that an additional drop ofgeometrical transparency can be relatively small.

In the described embodiments of the contaminant trap 10, 110, acontrolled uniform gas flow (for example argon) into a number ofseparated compartments Ch in vacuum environment can be achieved. Forexample, the uniformity be such that deviations are less than about 10%in argon mass per volume. The contaminant trap 10, 110 can function as astatic trap, which —for example—does not rotate with respect to thesource. It can function, for example, to “catch” Sn ions and atomscoming from the radiation source, wherein the trap 10, 110 can provide amaximum of radiation transmission. As follows from the above, for notrestricting radiation transmission, the gas injector can be designed tosubstantially extend in the volume which is formed by the “shadow path”of collector shells, and for example of a system of radially positionedmounting elements of the radiation collector.

The contaminant trap 10, 110 can be manufactured in various ways. Forexample, parts of a mentioned gas injector can be soldered or weldedafter the soldering or welding of the foils or plates 11. Besides, thegas injector and the foils or plates 11, 111 can be soldered or weldedin the same step.

For example, welding or soldering can be used for fine sheet metal partsof the gas injector, with wall thicknesses >0.1 mm. Also, electroformingcan be suitable, for example for the case that the wall thickness of thegas supply rings or ring sections are <0.1 mm. By using electroforming,there is freedom in the development of form. Besides, the gas injectorcan be provided with stiffening ribs, locally varying wall thicknessesor the like, for example to achieve a thinner wall thickness at gasoutflow openings for realizing the mentioned choking effect, and forproviding a higher wall thickness at global gas injector surface forimproved stiffness thereof. Also, different assembly methods can beused.

Besides, due to temperature differences, during normal performance andcleaning procedure, expanding and shrinking effects can be taken intoaccount for dimensioning the gas injector or manifold. For optimalradiation transmission, the gas injection rings or ring sections can bedesigned in the radiation-path at collector shell positions, such thatthey do not substantially block more radiation than the collector shellsthemselves. Preferably, the gas injector is designed such, that aminimum pressure-drop is reached through the gas supply rings 12, 112.Also, the gas injector rings or ring sections can be configured suchthat during use, thermal expanding and shrinking effects do not consumea certain tolerance budget. For example, during operation, whencollector shell and gas injector materials have reached their thermallyexpanded positions, they are preferably inline with respect to eachother, viewed along a radiation transmission direction.

During use, the gas injector can be exposed to relatively hightemperatures, for example an estimated environment temperature of 1500K.Therefore, preferably, the material of the gas injector preferably has ahigh heat resistance. Also, in an embodiment, the gas injector materialhas sufficient tensile strength at high temperatures, and can besuitable for welding, soldering or electroforming. Further, the materialpreferably meets a certain outgassing budget.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 mn), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below. For example, additional radial foilswith certain optimised configuration, can be installed between mainfoils in each contaminant trap channel. For example, such additionalradial foils can be installed near edges, at a far end of the trap, toincrease drag forces and to enable to achieve larger p(x)dx integralvalues.

1. An apparatus comprising: a radiation system including a radiationsource configured to produce a radiation beam; and a contaminant traparranged in a path of the radiation beam, the contaminant trapcomprising a plurality of foils or plates defining channels which arearranged substantially parallel to the direction of propagation of saidradiation beam, wherein the contaminant trap is provided with a gasinjector arranged to at least partially extend into or across at leastone of the channels and configured to directly inject gas at least attwo different positions into at least one of the channels of thecontaminant trap.
 2. An apparatus according to claim 1, wherein the gasinjector comprises a plurality of groups of spaced-apart outflowopenings, and wherein each group of spaced-apart outflow openings isassociated with one of said channels to supply gas to that channel. 3.An apparatus according to claim 2, wherein the outflow openings of eachgroup of spaced-apart outflow openings are located at different radialpositions with respect to the optical axis of the radiation beam.
 4. Anapparatus according to claim 2, wherein the outflow openings of eachgroup of spaced-apart outflow openings are located at different axialpositions with respect to the optical axis of the radiation beam.
 5. Anapparatus according to claim 2, wherein the outflow openings of eachgroup of spaced-apart outflow openings are connected, or connectable, todifferent gas supply lines.
 6. An apparatus according to claim 1,wherein the gas injector includes a plurality of substantiallyconcentric gas supply rings, or substantially concentric gas supply ringsections, and wherein each of the rings or ring sections comprisesdifferent gas outflow openings which are associated with differentchannels.
 7. An apparatus according to claim 6, wherein each of thesubstantially concentric gas supply rings, or substantially concentricgas supply ring sections, includes a plurality of the gas outflowopenings.
 8. An apparatus according to claim 6, wherein each of thesubstantially concentric gas supply rings, or substantially concentricgas supply ring sections, is provided with a plurality of gas injectioncapillaries, and wherein each of the gas injection capillaries includesat least one of the gas outflow openings.
 9. An apparatus according toclaim 1, wherein the contaminant trap is located between said radiationsource and a radiation collector, wherein the radiation collectorincludes a mirror surface that receives radiation from the radiationsource during use, and wherein the gas injector is configured tosubstantially not obstruct transmission of radiation from the radiationsource towards the mirror surface of the radiation collector.
 10. Anapparatus according to claim 1, wherein the gas injector includes asupersonic nozzle, which is configured to inject a supersonic gas streaminto the respective channel.
 11. An apparatus according to claim 1,wherein the contaminant trap includes at least about 100 channels. 12.An apparatus according to claim 11, wherein the contaminant trapincludes at least about 180 channels.
 13. An apparatus according toclaim 1, wherein the gas injector is configured to directly inject gasat least at four different positions into each of the channels of thecontaminant trap.
 14. An apparatus according to claim 1, wherein the gasinjector is configured to supply gas into at least one of the channelsof the contaminant trap under gas flow choke conditions.
 15. Anapparatus according to claim 14, wherein the gas injector includes atleast one gas supply tube having a wall which includes a plurality ofgas outflow openings, and wherein a length of each gas outflow openingis larger than a cross-section or diameter of that gas outflow opening.16. An apparatus according to claim 1, further including a gas supply tosupply gas to the gas injector, wherein the gas injector and the gassupply are configured to achieve: ∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m),during use, and wherein p(x) is the pressure at location x in thechannel, x1 is the position of the entrance of the channel and x2 is theposition of the gas outflow opening(s) in the channel.
 17. An apparatusaccording to claim 1, wherein the gas injector is arranged to inject gasin a direction which does not coincide with the radiation propagationdirection.
 18. An apparatus according to claim 1, further including atleast a first gas source which is connectable or connected to the gasinjector to supply at least a first gas thereto.
 19. An apparatusaccording to claim 18, wherein the first gas is argon.
 20. An apparatusaccording to claim 18, further including at least one gas supplier whichis configured to inject at least a second gas into a location near abutt-end of the contaminant trap, to catch, divert and/or deceleratefirst gas which flows out of that butt-end.
 21. An apparatus accordingto claim 20, wherein the second gas is helium.
 22. An apparatusaccording to claim 1, wherein the apparatus is provided with a drainsystem which is arranged to produce a transverse flow of gas in a radialand outwards direction with respect to the direction of propagation ofthe radiation beam and along an entrance of the contaminant trap, suchthat the transverse flow of gas comprises at least part of the injectedgas.
 23. A device manufactured by an apparatus according to claim
 1. 24.An apparatus according to claim 1, wherein the gas injector includes oneor more capillaries that extend within one or more of the foils orplates of the contaminant trap.
 25. An apparatus according to claim 1,wherein a group of main foils defines the channels, and wherein one ormore additional foils are installed between the main foils in at leastone of the channels.
 26. An apparatus according to claim 1, wherein thefoils or plates are oriented substantially radially with respect to anoptical axis of the radiation beam.
 27. An apparatus comprising: aradiation system including a source configured to produce a radiationbeam; and a contaminant trap arranged in a path of the radiation beam,the contaminant trap comprising a plurality of foils or plates definingchannels which are arranged substantially parallel to the direction ofpropagation of said radiation beam, wherein the foils or plates areoriented substantially radially with respect to an optical axis of theradiation beam, and wherein the contaminant trap is provided with a gassupply system arranged to at least partially extend into or across atleast one of the channels and configured to directly inject gas at leastat two different positions into each of the channels of the contaminanttrap.
 28. A device manufactured by an apparatus according to claim 27.29. An apparatus according to claim 27, wherein the gas supply systemincludes one or more capillaries that extend within one or more of thefoils or plates of the contaminant trap.
 30. An apparatus according toclaim 27, wherein a group of main foils defines the channels, andwherein one or more additional foils are installed between the mainfoils in at least one of the channels.
 31. A lithographic apparatuscomprising: a radiation system including a source configured to producea radiation beam; and a contaminant trap arranged in a path of theradiation beam, the contaminant trap comprising a plurality of foils orplates defining channels which are arranged substantially parallel tothe direction of propagation of said radiation beam, wherein thecontaminant trap is provided with a gas supply system which isconfigured to inject gas directly into each of the channels of thecontaminant trap, wherein the gas supply system is configured toachieve: ∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m), wherein p(x) is the pressureat location x in the channel, x1 is the position of the entrance of thechannel and x2 is the position of the gas outflow opening(s) in thechannel.
 32. A device manufactured by an apparatus according to claim31.
 33. An apparatus according to claim 31, wherein the gas supplysystem includes one or more capillaries that extend within one or moreof the foils or plates of the contaminant trap.
 34. An apparatusaccording to claim 31, wherein a group of main foils defines thechannels, and wherein one or more additional foils are installed betweenthe main foils in at least one of the channels.
 35. A contaminant trap,configured to be arranged in a path of a radiation beam during use, thecontaminant trap comprising a plurality of foils or plates definingradiation transmission channels which substantially transmit theradiation beam during use, wherein the contaminant trap is provided witha gas supply system arranged to at least partially extend into or acrossat least one of the channels and arranged to inject gas directly atleast at two different locations into at least one of the channels ofthe contaminant trap.
 36. A contaminant trap according to claim 35,wherein the gas supply system comprises a plurality of groups ofspaced-apart outflow openings, and wherein each group of spaced-apartoutflow openings is associated with one of said channels to supply gasto that channel.
 37. A contaminant trap according to claim 36, whereinthe outflow openings of each group of spaced-apart outflow openings areconnected to, or connectable to, different gas supply lines.
 38. Acontaminant trap according to claim 36, wherein the outflow openings ofeach group of spaced-apart outflow openings are located at differentradial positions with respect to the optical axis of the radiation beam.39. A contaminant trap according to claim 36, wherein the outflowopenings of each group of spaced-apart outflow openings are located atdifferent axial positions with respect to the optical axis of theradiation beam.
 40. A contaminant trap according to claim 35, whereinthe gas supply system includes a plurality of substantially concentricgas supply rings, or substantially concentric gas supply ring sections,and wherein each of the gas supply rings or ring sections comprisesspaced-apart gas outflow openings which are associated with differentradiation transmission channels to supply gas to these channels.
 41. Acontaminant trap according to claim 40, wherein the gas supply rings orthe ring sections are connected to each other by one or moresubstantially radially extending connecting parts.
 42. A contaminanttrap according to claim 41, wherein the substantially radially extendingconnecting parts are provided with one or more gas supply lines tosupply gas to the gas supply rings or to the ring sections.
 43. Acontaminant trap according to claim 40, wherein each of thesubstantially concentric gas supply rings or substantially concentricgas supply ring sections extends substantially perpendicular through thefoils or plates.
 44. A contaminant trap according to claim 40, whereinthe gas supply system includes at least two separate groups ofsubstantially concentric gas supply ring sections, which groups togetherform substantially closed rings.
 45. A contaminant trap according toclaim 44, further including one or more connecting parts which connectthe ring sections of each group of substantially concentric gas supplyring sections to each other at about their middles, measured along theircircumferences.
 46. A contaminant trap according to claim 35, whereinthe contaminant trap includes about 100 channels or more.
 47. Acontaminant trap according to claim 35, wherein the gas supply system isprovided with a plurality of gas injection capillaries, and wherein eachof the gas injection capillaries includes at least one gas outflowopening.
 48. A contaminant trap according to claim 35, wherein the gassupply system includes a supersonic nozzle, which is configured toinject a supersonic gas stream into the respective channel.
 49. Acontaminant trap according to claim 35, wherein the gas supply systemincludes one or more capillaries that extend within one or more of thefoils or plates of the contaminant trap.
 50. A contaminant trapaccording to claim 35, wherein a group of main foils defines thechannels, and wherein one or more additional foils are installed betweenthe main foils in at least one of the channels.
 51. A contaminant trapaccording to claim 35, wherein the foils or plates are orientedsubstantially radially with respect to an optical axis of the radiationbeam.
 52. A contaminant trap, configured to be arranged in a path of aradiation beam during use, the contaminant trap comprising a pluralityof foils or plates defining radiation transmission channels whichsubstantially transmit the radiation beam during use, wherein thecontaminant trap is provided with a gas supply system which is arrangedto inject gas directly at least at two different locations into at leastone of the channels of the contaminant trap, wherein the gas supplysystem is configured to achieve: ∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m) in eachof the channels, wherein p(x) is the pressure at location x in thechannel, x1 is the position of the entrance of the channel and x2 is theposition of the gas outflow opening(s) in the channel.
 53. A contaminanttrap according to claim 52, wherein the foils or plates are orientedsubstantially radially with respect to each other.
 54. A devicemanufacturing method comprising projecting a patterned beam of radiationonto a substrate, wherein: a source is provided to produce a radiationbeam; and a contaminant trap is provided in a path of the radiationbeam, wherein the contaminant trap comprises a plurality of foils orplates defining radiation transmission channels which substantiallytransmit said radiation beam, wherein gas is directly injected at leastat two different positions into at least one of the channels of thecontaminant trap via a gas injector arranged to at least partiallyextend into or across the at least one of the channels.
 55. A devicemanufacturing method according to claim 54, wherein the gas is beinginjected in an injection-direction which is different from a directionof propagation of said radiation beam through the contaminant trap. 56.A device manufacturing method according to claim 55, wherein the gas isbeing injected in transverse directions into the channels.
 57. A devicemanufacturing method according to claim 54, further including: producinga transverse flow of gas in a radial and outwards direction with respectto the direction of propagation of the radiation beam and along anentrance of the contaminant trap, such that the transverse flow of gascomprises at least part of the injected gas.
 58. A device manufacturingmethod according to claim 57, wherein the contaminant trap is providedbetween the radiation source and a collector for collecting theradiation, and wherein the method further comprises: providing acrossing gas flow across the radiation beam and in a directionsubstantially transverse the direction of propagation of the radiationbeam.
 59. A device manufacturing method according to claim 58, whereinthe gas that is injected into the at least one channel of thecontaminant trap is argon, wherein the crossing gas flow is a helium gasflow.
 60. A device manufacturing method according to claim 54, whereinthe gas is injected at least at four different positions directly intoeach of the channels of the contaminant trap.
 61. A device manufacturingmethod according to claim 54, wherein the gas is being injected at leastat two different radial positions in each of the channels, viewed fromthe optical axis of the radiation beam.
 62. A device manufacturingmethod according to claim 54, wherein the gas is being injected at leastat two different axial positions, viewed with respect to the opticalaxis of the radiation beam, in each of the channels of the contaminanttrap.
 63. A device manufacturing method according to claim 54, whereinthe gas is directly injected at least at two different positions intoeach of the channels of the contaminant trap, such that:∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m) is achieved in each of the channels,wherein p(x) is the pressure at location x in the channel, x1 is theposition of the entrance of the channel and x2 is the position of thegas outflow opening(s) in the channel.
 64. A device manufacturing methodaccording to claim 63, wherein the gas that is injected into eachchannel is argon.
 65. A device manufacturing method according to claim64, wherein the amount of argon that is injected into each channel isabout 10⁻⁶ kg per second or more.
 66. A device manufacturing methodaccording to claim 64, wherein the amount of argon that is injected intoeach channel is about 10⁻⁶ kg per second or less.
 67. A devicemanufacturing method according to claim 54, wherein the gas is suppliedto the at least one channel via at least two outflow openings of atleast one gas supply line, and wherein the dimensions of the outflowopenings and the gas pressures downstream and upstream of the outflowopenings are such, that the gas is supplied under choke conditions. 68.A device manufacturing method according to claim 67, wherein the gaspressure inside the supply line is at least twice the gas pressure inthe respective channel, downstream of the outflow openings.
 69. A devicemanufactured by a method according to claim
 54. 70. A devicemanufacturing method according to claim 54, wherein the foils or platesare oriented substantially radially with respect to an optical axis ofthe radiation beam.
 71. A device manufacturing method comprisingprojecting a patterned beam of radiation onto a substrate, wherein: asource is provided to produce a radiation beam; and a contaminant trapis provided in a path of the radiation beam, wherein the contaminanttrap comprises a plurality of foils or plates defining channels whichare arranged substantially parallel to the direction of propagation ofsaid radiation beam, and wherein gas is directly injected at least attwo different positions into each of the channels of the contaminanttrap via a gas injector arranged to at least partially extend into oracross each of the channels.
 72. A device manufacturing method accordingto claim 71, wherein the gas is directly injected at least at twodifferent positions into each of the channels of the contaminant trap,such that ∫_(x 1)^(x 2)p(x)𝕕x > 1  (Pa.m) is achieved in each of thechannels, wherein p(x) is the pressure at location x in the channel, x1is the position of the entrance of the channel and x2 is the position ofthe gas outflow opening(s) in the channel.
 73. A device manufacturingmethod according to claim 71, wherein the gas is being injected at leastat two different radial positions in each of the channels, viewed fromthe optical axis of the radiation beam.
 74. A device manufacturingmethod according to claim 71, wherein the gas is being injected at leastat two different axial positions, viewed with respect to the opticalaxis of the radiation beam, in each of the channels of the contaminanttrap.
 75. A device manufactured by a method according to claim 71.